How to prepare for a fasting blood test

For a fasting profile, avoid all food and calorie-containing drinks for 8 to 12 hours before sample collection. Plain water is allowed and actually helps — being well hydrated makes the vein easier to access.

Continue prescribed medicines unless your doctor has specifically advised otherwise, and mention every medication and supplement to the phlebotomist, since biotin, vitamin C and steroids can influence certain results. Avoid alcohol for 24 hours and heavy exercise on the morning of the test.

Morning collection between 7:00 AM and 9:30 AM is preferred because several hormones and glucose values follow a daily rhythm. Wear a sleeve that rolls up easily and plan to sit quietly for five minutes before collection.

If you feel faint during collection, tell the technician immediately — lying down for a few minutes resolves it in nearly all cases.